An extensive flow cytometric evaluation continues of patients with autoimmune lymphoproliferative syndrome (ALPS) and their extended family membershasw established expanded double-negative T-cell and B-cell populations. Double-negative T-cells have been demonstrated to be alpha beta TcR, CD57+, HLA-DR+, and CD45RA+. This study has been extended to characterize the double-negative T-cells more completely including B220 expression and gamma-delta TcR T-cells in all ALPS patients. In addition, B cells have been found to have dimished memory B cells based on a decreased level of CD27 expression accompanied by altered repertoire of immunoglobuine heavy chain expression and an expansion of CD5+ B cells. Immunoregulatory T cell appear to be present in normal numbers based on a quantitiative RTPCR assay for Fox P3 and normal intracellular Fox P3 staining by flow cytometry despite the depression CD4/CD25 T cells. We have identified increased levels of vitamin B12, soluble Fas ligand and IL-18 along with the previous observation of increased levels of plasma IL-10 in ALPS patients. We have just completed an extensive evaluation of the clinical and laboratory findings in 562 ALPS patients and their family members. This data has recently been compiled and submitted for publication. It revealsed that a level of double negative T cells above 4% together with an elevation of soluble FasL has a 97% predictive value for ALPS type 1a (Fas mutation) both germline and somatic associated mutations. In addition, having more than 16% B cells expressing CD27 (memory B cells) virtually excludes the diagnosis of ALPS. We are currently reviewing this data base in an attempt to define criteria that may differentiate between ALPS type 3 (no none mutation but a defect in Fas mediated apoptosis) and ALPS phenotype (clinical features of ALPS but no apoptotic defect detectable). The results of this evaluation could prove to be very valuable for clinicians seeing patients with ALPS like syndromes. We are also presently reviewing all of the Fas mutation data in order to update the ALPS database and are in the process of developing a reporting site for ALPS patient data through a collaboration with NCBI. We also just hosted an international symposium on ALPS in collaboration with our colleagues in NIAID.